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Old 01-23-2013, 09:13 PM   #1
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I am preparing to get my class b license as I live in Texas and it is required for my coach. In reading the study guide I came across this section in the air brakes chapter:

Quote:
Caution. Never push the brake pedal down when the spring brakes are on. If you do, the brakes could be damaged by the combined forces of the springs and the air pressure. Many brake systems are designed so this will not happen. But not all systems are set up that way, and those that are may not always work. It is much better to develop the habit of not pushing the brake pedal down when the spring brakes are on.
I have always held the foot brake when setting the park brake, releasing, or doing the brake test. What am I missing?
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Old 01-23-2013, 09:17 PM   #2
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Newer MH brakes have an anti-compounding setup in them so you don't need to worry about it. But you want to answer the test correctly so the booklet is correct in this case.
Both our 2000 and now 2002 have the correct setup so I don't worry.
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Old 01-23-2013, 09:37 PM   #3
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That is good to know. Thanks!

Do all the axles have a spring brake?
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Old 01-23-2013, 09:42 PM   #4
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That is good to know. Thanks!

Do all the axles have a spring brake?
No, just the rears, that's why you never lift the rear tires off the ground, it can roll or shift sideways. Don't ask how I know about shifting sideways
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Old 01-23-2013, 10:47 PM   #5
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Just the rear MAIN axle. Not the tag.
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Old 01-23-2013, 10:53 PM   #6
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Just the rear MAIN axle. Not the tag.
Yep, that true. We don't have a tag so I forgot that!
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Old 01-23-2013, 10:57 PM   #7
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Yep, that true. We don't have a tag so I forgot that!
The one he has on order does, so I thought it was worth mentioning.
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Old 01-23-2013, 10:58 PM   #8
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And the parking brake is that spring brake right? I guess nothing is different from my assumptions just that paragraph threw me for a loop.

Thanks all!
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Old 01-23-2013, 11:04 PM   #9
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And the parking brake is that spring brake right? I guess nothing is different from my assumptions just that paragraph threw me for a loop.

Thanks all!
Yes, the parking brake is the spring brake. It's held open by air pressure. So when you loose air, the spring closes it and stops you. Suddenly, I've heard. Never tried it myself.
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Old 01-24-2013, 04:22 AM   #10
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Quote:
Originally Posted by redbaron73 View Post
I am preparing to get my class b license as I live in Texas and it is required for my coach. In reading the study guide I came across this section in the air brakes chapter:



I have always held the foot brake when setting the park brake, releasing, or doing the brake test. What am I missing?
That would have thrown me off too. How can this be true, if you have 90 pounds of air in all your tanks, then all you're doing is applying the same 90 pounds to the two chambers (service and park) (ie not 180 pounds)??

And I would also think it makes perfect sense to apply service brakes be4 releasing park brakes to prevent movement especially if you're on a hill??

I just renewed my air brake endorsment and would have missed that question, but then again we're allowed 4 wrong out of 20...
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Old 01-24-2013, 04:51 AM   #11
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And I would also think it makes perfect sense to apply service brakes be4 releasing park brakes to prevent movement especially if you're on a hill??

..
and the reverse of that too ... wouldn't you hold the RV in position with the foot brake before engaging Park?
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Old 01-24-2013, 07:24 AM   #12
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Even if the rig didn't have the anti-compounding system fitted, the normal engineering factors of safety designed into every component (especially critical components like braking systems) would allow for applying reasonable pedal pressure while applying the parking brake at the same time. The advice is normally expressed as not to apply FULL pressure on the pedal rather than not to apply ANY pressure which would clearly be impractical.
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Old 01-24-2013, 09:59 AM   #13
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Yes, the parking brake is the spring brake. It's held open by air pressure. So when you loose air, the spring closes it and stops you. Suddenly, I've heard. Never tried it myself.
Done at the Freightliner course in Gaffney, SC

The answer to the bold portion above will surprise you. I have been in a rig that the emergency air brakes were tested at about 45 mph, as were the foot brake at about 25 mph.

In the case of the foot brake there is a sudden violent stop if they are engaged with heavy foot pressure. All wheels become engaged when braking with the foot brake. It can send things flying. Hold on tight.

As for the emergency pull you will come to a quick gradual stop. Quite different from a full force pressure on the foot brake. Depending on speed it will take quite a distance in comparison to the foot brake. When the emergency brake is applied, only the rear wheels are engaged, and that is quite a difference. I was pleasantly surprised. Oh. and with the TOAD pushing the rig it will be even a greater distance. Everyone should experience it at least one time in a practice session. I hope no one ever has to use the "park" brake while going down the highway.

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and the reverse of that too ... wouldn't you hold the RV in position with the foot brake before engaging Park?
Personally, unless you are on a ground area that is completely level, I think it is a dangerous thing to not have one or the other braking systems engaged. So, when we park and I am ready to leave my driving seat, I start releasing the brake pedal at the same time I am setting the the parking brake. I really believe I still have full control.

The reverse is true when departing. As I release the emergency brake I am starting to engage the foot brake. With all the safety measures of the manufacturer in place and the way I do it just gives me peace of mind.

Now, for the emergency parking brake. One of the things that is taught at the Freightliner Course is in regards to "us" traveling down the highway and something happens to the driver. How does the co-pilot stop the vehicle. The simple answer, which is more thoroughly covered in the course is for the copilot to release the cruise control and pull the "yellow" triangle parking brake control while holding the steering wheel on course. The motorhome will come to a quick gradual stop. It is definitely not a time to worry about traffic behind you. But during this time if one has the presence of mind to do so, then pull as far over to the right on the shoulder as possible.

Happy trails.
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